Open coil heaters, as designed in accordance with the prior art, use a standard, single resistance wire, and in such design a good part of the cost of the heater is reflected in the cost of the resistance wire. The criteria for selecting the gage of the resistance wire is related to the surface area of the wire. By choosing a larger gage wire, it is possible to reduce the operating temperature of the wire, and heretofore a size and has selected of sufficiently large gage to provide adequate life for the heater for a particular application. However, this unduly increased the cost of the heater.
I have discovered that the cost of the heater may be materially reduced by using a plurality of strands of smaller gage wire or flat ribbon wire in place of the single larger gage wire, since the weight of the resistance wire is reduced by about one-half.
However, the problem encountered in the use of fine braided wire is one of support since such wire is relatively flimsy. I have found that if at least one of the fine wires is formed of a material that will withstand the heat generated, sagging of the fine Heat-generating wires is minimized. The wires are supported in an economical manner by projecting insulated members through the open spaces of the loosely braided wires at various places along the reaches of the wires, the insulated members being secured to a frame support.